考虑静水压力和LODE 角的塑性模型 在GH4169 合金上的应用

针对典型盘用镍基高温合金GH4169,采用Bai-Wierzbizki(B-W)塑性理论对其塑性变形行为进行建模和应用评估。B-W塑性理论假设金属材料塑性变形仍服从von Mises屈服准则,但屈服函数考虑了静水压力和LODE角(偏应力第3不变量)对塑性行为的影响。采用Abaqus/Explicit商业有限元软件编制了该塑性模型的用户材料子程序,设计开展了GH4169合金的光滑、缺口圆棒和缺口平板拉伸试验,基于有限元分析和优化方法确定了B-W模型相关材料参数,对GH4169合金光滑和缺口拉伸响应曲线进行有限元预测,并与试验结果进行对比分析。结果表明:B-W模型预测的GH4169合金缺口圆棒和平板拉伸响应曲线与试验结果非常吻合,而基于传统von Mises塑性模型预测的GH4169合金缺口拉伸响应曲线均明显高于试验曲线。     

复杂应力状态下金属材料屈服模型及有限元验证

日益复杂的结构细节特征和载荷作用给飞机金属实体结构的精细化设计提出了极高挑战,对复杂应力状态下金属材料的屈服及失效行为的高精度预测是结构精细化设计与验证的关键。多种典型构形拉伸试验研究发现基于单一曲线假设的 von Mises 屈服理论难以精确描述金属材料在复杂三维应力状态下的屈服行为。为提高复杂应力状态下金属弹塑性行为的预测精度,提出一种基于应力三轴度和 Lode 角参数修正的 von Mises屈服模型,将该修正模型以 VUMAT 用户材料子程序嵌入 ABAQUS/explicit 求解器对铝合金 2024-T4 试件的屈服行为进行数值模拟。结果表明：本文提出的修正屈服模型比 von Mises 屈服模型更符合试验结果。     

某镍基单晶高温合金塑性变形与失效分析

为有效预测某镍基单晶高温合金在复杂应力状态下的塑性变形响应,采用光滑平板拉伸试验获取[001]向拉伸性能,根据缺口平板试件试验数据反衍优化获得其他取向的性能参数,基于广义Hill准则,构建了针对该材料的各向异性弹塑性本构模型,并使用该模型开展镍基单晶高温合金在复杂应力状态下的塑性变形行为的大变形有限元预测,结合Freudenthal失效准则对名义极限强度进行预测,与试验结果进行对比分析。结果表明:反衍优化建立的各向异性本构模型能够较为准确地描述该镍基单晶高温合金在复杂应力状态下的拉伸响应行为,且能较为准确地预测出几种试件的名义极限强度,误差小于6%。对工程中单晶涡轮叶片塑性失效分析有一定指导意义。     

非晶合金的弹塑性本构关系研究

为了将大块非晶合金塑性本构方程拓展到多维应力空间 ,对Zr41.2 Ti13 .8Ni10 Cu12 .5Be2 2 .5大块非晶合金进行了拉压和扭转剪切实验研究。对实验结果的深入分析表明了该材料具有Mises强化特性。应用连续介质力学的弹塑性理论 ,对材料的屈服变形行为进行了研究 ,借助材料的压缩实验和剪切实验资料 ,推导出多维应力状态下大块非晶合金的塑性本构关系的 2种表达式。证明了 2种表达式的统一性。     

镍基单晶合金弹塑性本构模型

Hill模型用于面心立方单晶的弹塑性变形,在描述屈服特性的晶向相关性时精度不高。考虑正交各向异性材料在偏轴受载时存在拉、剪应力耦合效应的影响,通过增加一项由应力偏张量分量的二次项乘积构成的应力不变量,对Hill屈服模型进行修正,并根据单晶合金的屈服特点提出了新的单晶合金屈服准则。用该屈服准则对DD3单晶合金的屈服应力进行预测,760℃时能很好地符合试验结果;与Hill屈服准则比较,预测精度显著提高。在此基础上,重新定义了适合新屈服准则的等效应力,并由联合流动法则,以屈服函数作为塑性势函数,采用等向硬化模型,建立了单晶合金的弹塑性本构模型,推导出相应的弹塑性矩阵。对于各向同性材料,新屈服准及其等效应力则退化为VonMises屈服准则和其相应的等效应力。      

各向异性多轴近似应力应变分析方法研究及应用

用基于Neuber法则的各向异性多轴近似应力应变分析方法,计算了沿不同方向加载时,定向凝固合金DZ125和单晶DD6材料缺口构件,弹塑性应力应变分布以及应力集中处的弹塑性应力-应变响应.同时,将微分形式的、考虑了时间效应的Neuber法则拓展到各向异性多轴保载情形,给出了拉伸保载时缺口根部的应力-应变响应.计算结果显示,单轴循环模拟结果与试验数据吻合,缺口构件循环加载以及拉伸保载预测结果与物理实际相符.证明了基于Neuber法则的各向异性多轴应力应变分析方法,可用于国产定向凝固合金和单晶材料循环加载以及拉伸保载分析.      

固体推进剂双向拉伸试件优化设计及试验

基于Kelly提出的十字形试件,设计了一种新型固体推进剂双向拉伸试件。利用ANSYS有限元软件对试件双向加载过程试验区中引起的应力应变的数值模拟,实现了十字形试件的优化设计,经过优化的试件在满足双轴试验要求方面有了明显的改进。通过对丁羟复合固体推进剂试件双向加载力学行为试验研究,获得不同拉伸速率双向拉伸应力—应变破坏曲线,为推进剂材料破坏分析的经验准则提供判据。结果表明,固体推进剂断裂延伸率的双向弱化效应很明显,双向加载比例为等双拉状态时,其双向断裂延伸率比单向断裂延伸率降低37.5%。     

一种广义Bodner-Partom黏塑性本构模型

针对Bodner-Partom黏塑性本构模型描述合金材料的率相关塑性和循环硬化行为时精度不足的问题,在无屈服面统一黏塑性本构理论框架内对其进行了改进：利用塑性势函数重塑了流动法则,摆脱了Mises材料的限制;在内变量演化方程中引入塑性应变率修正项并由非线性因子控制,拓展了不同的硬化/恢复演变方向。利用FGH96合金在550℃下的单轴拉伸及低周疲劳试验数据将广义B-P模型与原始B-P模型进行了对比验证,结果表明本文模型的模拟效果与材料非弹性特征吻合良好,具有克服应力应变滞回曲线“过方”问题和表达平均应力循环松弛的能力。模型对不同硬化机制的考虑对于高温合金材料更具优越性。     

ZSGH4169合金细观力学行为的数值模拟

基于晶体塑性本构理论,利用多晶代表性单元从细观尺度研究了ZSGH4169合金在650℃条件下考虑双轴应力状态的循环应力应变行为.计算结果表明:该合金在双轴拉伸应力控制下存在与低周疲劳试验常用的单轴应力状态一致的棘轮效应.对两种应力状态下的结果进行对比发现,在1150MPa应力单轴循环载荷下初始循环残余应变比双轴应力状态高出3倍,且双轴应力状态下最终循环稳定,残余应变约为1.2%,但在单轴应力状态下是不稳定的.对应力和塑性应变累积不均匀性的分析表明:单轴和双轴拉伸状态下,虽然应力和应变分布的不均匀性都随着循环数的增加而增加,但单轴拉伸状态下平均应力随循环数增加,而双轴拉伸状态下几乎为常数.      

复杂载荷下疲劳寿命估算

 本文给出了LY12CZ铝合金板材的循环硬化规律;以材料在循环载荷作用下累积的塑性滞后能作为疲劳损伤准则,证明了应力控制等幅循环加载条件下损伤累积随循环次数变化的非线性,导出了材料瞬态塑性应变能的计算公式,算出了破坏发生时材料耗散的总塑性应变能,并给出了它与应力变程的关系。文中把疲劳损伤分为静拉伸损伤与循环损伤两部分,给出了损伤累积模型。以该模型为基础,计算了两级加载、4级加载和程序加载下光滑试件的疲劳寿命。计算结果与试验结果符合很好。     

Damage characteristics and constitutive modeling of the 2D C/Si C composite: Part I – Experiment and analysis

This paper reports an experimental investigation on the macroscopic mechanical behaviors and damage mechanisms of the plain-woven(2D) C/Si C composite under in-plane on- and offaxis loading conditions. Specimens with 15, 30, and 45 off-axis angles were prepared and tested under monotonic and incremental cyclic tension and compression loads. The obtained results were compared with those of uniaxial tension, compression, and shear specimens. The relationships between the damage modes and the stress state were analyzed based on scanning electronic microscopy(SEM) observations and acoustic emission(AE) data. The test results reveal the remarkable axial anisotropy and unilateral behavior of the material. The off-axis tension test results show that the material is fiber-dominant and the evolution rate of damage and inelastic strain is accelerated under the corresponding combined biaxial tension and shear loads. Due to the damage impediment effect of compression stress, compression specimens show higher mechanical properties and lower damage evolution rates than tension specimens with the same off-axis angle. Under cyclic tension–compression loadings, both on-axis and off-axis specimens exhibit progressive damage deactivation behaviors in the compression range, but with different deactivation rates.     

双轴拉伸应力下后继屈服面的演化研究

屈服面的位置和形状直接影响着材料塑性应变的确定。针对双轴拉伸应力下金属材料的塑性行为,以一种弹塑性损伤本构理论为基础,研究了后继屈服面在拉-拉应力空间中的演化。考虑了有限变形效应和耦合硬化效应,给出了屈服面的确定方法,并预测了拉-拉应力空间中的初始屈服面(IYS)和后继屈服面,预测结果显示本文提出的理论模型能一致描述出后继屈服面演化中的前端尖点效应、尾部包氏效应、膨胀/收缩以及移动和畸变。针对两种加工硬化材料(Al 6061-T 6511和Annealed 1100 Al)承受轴向拉伸、环向内压、轴向-环向混合比例加载时的后继屈服面,将模型预测的结果与文献中的实验结果进行对比。结果表明,所提模型能较好地预测后继屈服面的演化,并能分析其物理机制,为后继屈服面的演化研究提供了一种可行的方法。     

Biaxial tensile behavior of Ti-6Al-4V under proportional loading

The biaxial tensile behavior of isotropic Ti-6Al-4 V is characterized in this paper. A novel cruciform specimen was designed and optimized to achieve uniform stress and strain distribution within the gauge area. Biaxial tensile tests were conducted at three different loading ratios by the biaxial testing machine. The Digital Image Correlation (DIC) technique was applied to determine strain distribution, and a high-speed camera was employed to record the fracture process. An Inverse Analysis (IA) approach with a combined experimental and numerical method was proposed to determine the true stresses at the gauge section of the specimen during biaxial tensile tests. The results indicate that the initial yield locus can be described by the Cazacu criterion accurately, whereas the Mises criterion can predict better the strengthening behavior of Ti-6Al-4 V in the first quadrant in the principal stress space.     

Yield anisotropy and tension/compression asymmetry of a Ni3Al based intermetallic alloy

In order to investigate the yielding behavior of the newly developed Ni 3 Al-based intermetallic alloy IC10, yield stresses have been measured in tension and compression with different orientations. The specimens were cut from a sheet with different angles inclined from the solidification direction. The inclined angles were taken to be 0 , 22.5 , 45 , 67.5 and 90 . All experiments were conducted at room temperature except for orientation 0 , whose deformation temperatures ranged from 298 to 1273 K. Experimental results show that the yield strength of alloy IC10 has the anomalous behavior which has been observed for other Ll 2 -long-range ordered intermetallic alloys, but it is less pronounced. The abnormalities show the following characteristics: (i) the yield strength increases as the temperature is raised below the peak temperature, (ii) yield strength anisotropy, (iii) tension/compression asymmetry. Compared to Ni 3 Al single crystals, the polycrystalline exhibits some different yielding behaviors which may be due to the high volume fraction of c phase.     

Influence of uniaxial tensile pre-strain on forming limit curve by using biaxial tensile test

This paper focused on the effect of pre-strain on forming limit curves (FLC) of 5754-O aluminum alloy sheet through utilizing biaxial tensile approach. Based on Swift model and Yld2000-2d yield criterion, the dimensions of cruciform specimen was optimized through applying finite element method for increasing the strain at specimen center. After that, with the recommended specimen size, the cruciform specimen was tested under various stroke ratios to experimentally characterize the limit strains under different pre-strain levels. Subsequently, the biaxial tensile tests were simulated by Abaqus to obtain the limit strains and validate the material models. It can be observed in both experiments and simulations that the pre-strained uniaxial tension followed by plane tension or equi-biaxial tension can improve the formability of sheet metals. Besides, the strain path change affects the trend of first derivative of strain rate difference between neighboring points with respect to time. An early increase occurred and then fell back to the stable value, the steady evolution continued until to a new increase reaching the critical value. The M–K prediction approach was simulated to verify the influence of pre-strain on FLC. It can be found that the early increase peaks of the major strain incremental ratio rose with the amplitude of pre-strain. Finally, the phenomenon of pseudolocalization caused by the strain path change was explained through evolution of stress state inside the groove.     

LC4铝合金厚板的塑性变形各向异性

 LC4铝合金厚板的塑性变形具有明显的各向异性。本文提出一种表示各向异性的方法及其随纵向应变和热处理状态的变化,并观察了断口形态。     

板料异向性对拉深成形的影响

推导出了异向性板料在两向应力状态下的塑性方程，分析了厚向异向性和面内异向性对拉深成形的影响，提出了利用异向性现象来提高拉深工艺水平的途径。     

一种镍基单晶合金多轴低周疲劳损伤参量

用损伤应变能释放率作为热力学广义力描述正交各向异性材料的疲劳损伤过程,定义了含有3个弹性常数的镍基单晶应力三轴性因子,它不仅反映多轴载荷下的复杂应力状态,还显示正交各向异性材料偏轴受载时存在的正应力与剪应力的耦合效应,是对各向同性材料应力三轴性因子的拓展。用镍基单晶应力三轴性因子修正Mises应变范围作为疲劳损伤参量,引入损伤驱动力循环特征参数反映循环载荷的交变特性,提出了单晶合金低周疲劳损伤模型。利用DD3和CMSX-2单晶合金低周疲劳试验数据,采用多元线性回归分析方法拟合疲劳损伤模型参数,试验所得数据都落在2倍和2.5倍偏差分布带内。      

Damage characteristics and constitutive modeling of the 2D C/SiC composite: Part Ⅱ–Material model and numerical implementation

In this work, a macroscopic non-linear constitutive model accounting for damage, inelastic strain and unilateral behavior is proposed for the 2D plain-woven C/Si C composite. A set of scalar damage variables and a new thermodynamic potential expression are introduced in the framework of continuum damage mechanics. In the deduced constitutive equations, the material's progressive damage deactivation behavior during the compression loading is described by a continuous function, and different deactivation rates under uniaxial and biaxial compression loadings are also considered. In damage evolution laws, the coupling effect among the damage modes and impediment effect of compression stress on the development of shear damage in different plane stress states are taken into account. Besides, the general plasticity theory is applied to describing the evolution of inelastic strain in tension and/or shear stress state. The Tsai–Wu failure criterion is adopted for strength analysis. Additionally, the material model is implemented as a user-defined material subroutine(UMAT) and linked to the ABAQUS finite element software, and its performance is demonstrated through several numerical examples.